Noob question: Solving crash problems

[JumbledGrass]

Software
XBian version: 1.0RC2
XBMC version: 13 newest (auto updates are on)
Overclock settings: 900

Hardware
Power supply rating: 5V
RPi model (model A/B 256mb/512mb): B 512
SD card size and make/type: Integral 16GB Class 10
Network (wireless or LAN): LAN
Connected devices (TV, USB, network storage, etc.): Samsung CEC-capable TV, USB HDD

I sometimes come home to find my Pi has stopped responding to network, isn't showing as a source on my TV and the hard drive is silent, although the lights (all of them) are steadily lit on the board. I pull the power and it's back up and running. It's a mystery as to what process has caused the death.

Question is, where does one usually go to begin investigating the cause of these sorts of problems? Is there a log somewhere that would give me a clue?

I don't necessarily want help walking through this specific issue with anyone here (unless there's a known and glaringly obvious solution) but to try and solve it myself. I might also look on the main RPi forum.